Dagur the Deranged

Dagur the Deranged is a former villain and archenemy-turned-ally of Hiccup and the Dragon Riders in DreamWorks Dragons: The Series, and the Chief of the Berserker Tribe. Later, in Dragons: Race to the Edge, he proves himself changed and does everything he can to help the Dragon Riders, which includes seemingly sacrificing himself to prevent them from taking on a suicide mission.

Shortly after saving Shattermaster from the Dragon Hunters, Dagur ends up becoming a full-time dragon rider. He eventually gains Sleuther as his second dragon and later on marries Mala and becomes King of the Defenders of the Wing tribe, uniting it with the Berserker Tribe.